1. Field of the Invention
The present invention relates generally to the field of building construction from prefabricated building elements, such as prefabricated concrete building walls and modules. More specifically the present invention relates to a portal form for placement within the wall form perimeter wall of a building wall form, to define an opening in the resulting concrete wall for mounting a window or a door. The portal form includes a portal form perimeter wall configured as a closed loop which is preferably either square or rectangular and prevents concrete poured into the wall form from flowing into the space encompassed by the portal form, and includes form spacing and dislodgement screw structures including spacing screws which are rotated after the wall concrete cures, to space the portal form from the wall form bottom wall and thereby dislodge the portal form from the grip of the cured concrete. The portal form perimeter wall has a wall upper edge and a wall lower edge and either the entire portal form perimeter wall, or only its outer surface is tapered inwardly from the wall upper edge to the wall lower edge for greater ease in dislodging and removing the portal form from the cured wall concrete. The portal form perimeter wall or its outer face is preferably stepped to define window and door mounting in the resulting door or window opening.
2. Description of the Prior Art
There have long been forms for receiving uncured concrete to create a pre-fabricated concrete wall. Interior forms have been provided for forming windows and door openings. Yet interior forms have either been very difficult to remove from the cured wall or have necessarily remained as part of the cured wall.
Callan, U.S. Pat. No. 2,557,631, issued on Jun. 19, 1951, discloses a collapsible form for forming window or door openings in concrete walls. The Callan portal form is fragmented into form segments and includes a dislodgement mechanism which pulls the form segments inwardly toward the center of the portal form, but does not space the portal form from the wall form bottom wall. Callan is complex and as a result would be expensive to manufacture and subject to mechanical failure.
It is thus an object of the present invention to provide a window and door portal form for placement within a concrete wall form for defining an opening in the cured concrete wall for placement of a window or a door.
It is another object of the present invention to provide such a portal form which includes means for progressively, evenly and reliably dislodging the portal form from the cured concrete wall.
It is still another object of the present invention to provide such a portal form which can be used again and again.
It is finally an object of the present invention to provide such a portal form which inexpensive to manufacture, durable, removably with a common tool such as an air wrench by a workman of ordinary skill.